Separation of ferrosilicon from magnetite by froth flotation



Patented Aug. 19, 1952 SEPARATION 'OF FERROSILICON FROM MAGNETITE BY FROTH FLOTATION Swain Joseph Swainson, Darien, Conn., Earl Conrad Herkenhoff, Hibbing, Minn., and Richard Harold Lowe, St. Louis, Mo., assignors to American Cyanamid Company, New York, N. Y., a

corporation of Maine No Drawing. Application August 26, 1949, Serial No. 112,648

7 Claims.

This invention relates to a process of separation by froth flotation of finely divided magnetite from finely divided ferrosilicon in used media, which have been employed in the sink and float separation of fragmentary material. The invention also includes a method of adjusting the gravity of mixed magnetic media for the heavy-media separation of ores containing magnetizable solids, which contaminate a ferrosilicon medium.

- Be'neficiation of ores by sink and float processes usingheavymedia plays a prominent part in ore dressing. The most commonly used heavy media are water suspensions of finely divided particles of magnetizable material. The two most important kinds of medium solids are magnetite and ferrosilicon. Magnetite would be ideal from the standpoint of rust resistance, ready availability, cheapness, hardness, and the like, but for the fact that the specific gravity of magnetite is too low for many heavy media separations, notably for the beneficiation of iron ores. Where a higher gravity medium is desired, ferrosilicon is normallyused in spite of its higher cost. Sometimes ferrosilicon isused alone, in other cases it may be used in admixture with magnetite. For iron ore beneficiation and similar treatments calling for a medium of high specific gravity, the amount of magnetite which can be admixed without encountering'excessive viscosity is about 25 to at most, 35%. In the case of some operations the amount of magnetite which can be tolerated is still lower.

Difiiculties are sometimes encountered when a ferrosilicon or mixed ferrosilicon-magnetite medium is used with ores which contain magnetite, and other natural magnetics such a pyrrhotite, or where mixed media are used under conditions which may result in losing more ferrosilicon than magnetite, as for example, by hydrolysis of FeSi. Where ores containing natural magnetic minerals, such as magnetite and pyrrhotite, are being treated, there is a tendency for these fine magnetic particles to build up in the medium because they normally are not rejected by the medium cleaning system. In such cases the medium gradually builds up a content of finely divided magnetite and afterthis content has passed the p81- missible limit themedium becomes useless. The magnetic cleaning circuit which is customarily used does not help because both magnetite and ferrosilicon and other magnetics which may be 2 present are recovered by the magnetic cleaners. The contamination of media with finely divided magnetite is thus a serious practical matter in heavy media installations.

The present invention is based on the discovery that the flotation characteristics of magnetite and ferrosilicon in used or contaminated heavy media are entirely different from the behavior of these materials in the ordinary state and, in fact, result in a reverse of flotation characteristics.

When fresh ferrosilicon alone is subjected to froth flotation with an anionic collector, it floats very readily. Magnetite alone is floated less readily under the same conditions. When a 50/50 mixture of fresh ferrosilicon and magnetite is subjected to froth .flotation with anionic collectors, the separation generally is non-selective but the ferrosilicon tends to float ahead of the magnetite.

Used heavy media containing magnetite and ferrosilicon, that is to say, media which have been in operation for some time in a plant separating ores by the sink and float process, give an entirely different result, but only with certain particular anionic promoters. The results are just the opposite of those obtained with fresh magnetite and fresh ferrosilicon. Instead of the ferrosilicon ShOWillg an ability to float as great or greater than that of magnetite, the mag-netite floats to give a very high-grade magnetite concentrate containing very little. ferrosilicon, and a tailing is obtained containing the bulk of the ferrosilicon and only a small amount of magnetite.

The anionic promoters useful in the present invention are sulfonated' reagents taken from four classes: The oil-soluble petroleum sulfonates from the refiningof petroleum lubricating oil; the water-soluble petroleum sulfonates obtained from the same source; sulfonated fatty acids; and sulfonated glyceride oils. The sulfonated fatty acids may advantageously be obtained from mixtures, some of them quite crude, such talloel, residues such as cotton seed foots, coconut oil foots and similar mixtures containing fatty acids obtained in the refining of glyceride oils. The sulfonated glyceride oils include such products as sulfonated castor oil, sulfonated tea seed oil,-sulfonated corn oil, and the like.

The effectiveness of this type of sulfonated reagent when used in the flotation of iron ore under conditions specified is well known and is described and claimed in the following patents to Booth and Herkenhofi: 2,385,054, issued September 18, 1945; 2,410,376 and 2,410,377, both issued October 29, 1946; 2,414,714, issued January 21, 1947; 2,433,258, issued December 23, 1947; 2,439,200, issued April 6, 1948, and 2,475,581, issued July 12, 1949.

With all of the reagents except oil-soluble petroleum sulfonates the condition must be at high solids for good results. With the oil-soluble petroleum sulfonates, however, it is possible to ob tain acceptable results if the conditionin is not effected at such high solids. In general, the exact solids content during conditioning is not critical and may be selected in the range'of 50 to 75% solids. Results, are a little better at the high end than at the low end although usable results are generally obtainable throughout the'range.

atoms It is not known why the flotation characteris I tics of magnetite and ferrosilicon are so drastically changed by the use of the materials in a heavy media separation process. It seems reasonably certain that somethin in the separation process must alter the. surface of the magnetite and ferrosilicon to change their flotation characteristics so drastically. It has not been possible hitherto, however, to determine the nature of this surface change .loy ordinary observation, such as microscopic observation. It is, therefore, not intended to limit the invention to any particular theory of just what the surface change is. It is also not known why the change of the surface in use as a heavy 'media should alter flotation characteristics only with a certain class of anionic. promoters, because other anionic promoters for iron minerals, such as fatty acids, do not give a selective float with used heavy media. It is only when the sulfonated promoters are used with acid conditioning that the anomalous results of the present invention are obtained. Here, again, the reasons for the phenomenon are not fully known, and it is not desired to limit the invention to any particular theory. It seems probable that the alteration of the surface by use in heavy media operations changes the characteristics toward acid conditioning. Otherwise it is difficult to understand why the surface alteration will give a highly selective magnetite float with the procedure of the present invention but will give a non-selective float with other well known anionic promoters.

There does not appear to be a sudden change in the characteristics of the magnetite and ferrosilicon. particles as they are used in heavy media operations. On the contrary, the change appears to be one that proceeds at a fairly slow rate with time. A mixed magnetite-ferrosilicon heavy medium which has been used for only a few minutes, or even an hour or so, behaves very much as does a fresh mixture of magnetite and ferrosilicon. Longer use, accompanied by attrition during circulation, and the use of lime, gradually changes the flotation characteristics of the medium until the great selectivity of the magnetite float with the sulfonated reagents of the present invention becomes apparent. This gradual transformation of the medium is further evidence that what is actually taking place is some change in the surface characteristics of the particles, particularly in the ferrosilicon. This is borne out by the fact that the time it takes for a magnetite-ferrosilicon medium to become sufli- 4 ciently altered so that a highly selective mag netite float results, will vary to some extent with the nature of the ferrosilicon particles originally in the medium, with the degree of agitation, and particularly with the nature of the fragmentary material treated. These variations are entirely consistent with a change resulting in surface alteration, though they are not definite proof thereof.

On the other hand, if the used medium has been permitted to air-dry or otherwise oxidize, whereby the ferrosilicon particles become seriously rust-filmed, the selectivity between the magnetite and ferrosilicon is greatly impaired.

The fact that the present invention is applicable only to spent or contaminated heavy media is not a practical drawback because, ordinarily, it would not be necessary to effect any major readjustment in the ratio of magnetite and ferrosilicon in fresh media. The balance is only gradually upset in use and therefore the present invention is applicable in practically all cases where a mixed magnetite-ferrosilicon medium has become unsuitable for further use.

It is an advantage that the flotation procedure of the present invention does not differ materially from standard flotation operations with sulfohated reagents on ordinary iron ores. It is not necessary to learn any new techniques, nor is the operation unduly critical. However, it must be realized that contaminated heavy media may contain a much higher concentration of magnetit than do many ores. It is, therefore, necessary in most cases to use more reagent, which is in accordance with general flotation practice and does not involve any particularly critical operation.

The behavior of differentpetroleum sulfonates will vary with their origin and with their chemical nature. There is, however, some difference in the relative effectiveness of the different sulfonates when used in the present invention. Thus it has been found that the lowest loss in ferrosilicon will often be obtained with water-soluble petroleum sulfonates, whereas, in. the flotation of ordinary iron ores, the higher-soluble petroleum sulfonates are not generally more eflicient. In the present invention the higher-soluble petroleum sulfonates are more active and can be used in small amounts but in many cases do not show quite so high a differential selectivity.

The present invention does not differ sharply from the froth flotation of ordinary iron ores. The acidity of the pulp should be such that on dilution to froth flotation density and floatin the rougher tailing, in the absence of added alkali, shows a pH in the range of 2 to 6. In addition to inorganic acids, certain strong organic acids may also be used. Typical. suitable acids are sulfuric, hydrochloric, nitric, hydrofluoric, phosphoric, acetic, and the like. However, sulfuric acid gives such generally excellent results and is so much cheaper thanthe other acids that it is preferred. The acid used in conditioning can be any strong inorganic acid which has a dissociation constant no less than 10*".

Contaminated heavy media often contain a considerable amount of slime unless 'flrst ma netically cleaned. It is desirable to deslime where the slime content is considerable. In this respect the flotation operation of the present invention follows conventional teachings. When the slimes have been removed in magnetic cleaning, of course, desliming is. not necessary. In

such cases it is often desirable to demagnetize before flotation.

The petroleum sulfonates used inthe present invention are not pure products. The compositions are somewhat indefinite and are ordinarily considered to be mixtures containing both sulfonates and sulfate esters. In the industry they are generally referred to as petroleum sulfonates and this term is used in the present specification and claims in this somewhat looser sense. i

In the examples and in the claims the term used magnetite-ferrosilicon media'is intended to cover a used medium for which the present invention is suitable; that is to say, one which has been used for a sufficiently long time so that the surface alteration of the particles, or whatever else causes the difference in floatability of the minerals, has been sufficiently effected. It does not include media which have been used for a very short time, and which do not differ materially in nature from fresh media, nor does it include media in which the ferrosilicon has oxidized upon standing or drying in open air.

In the claims, the term sulfonated collector will be used in its ordinary sense to cover the petroleum sulfonates and sulfonated glycerides and fatty acids, although these compounds contain, in many cases, sulfate groups instead of, or in addition to, sulfonate groups. The term petroleum sulfonate is used to cover the oilsoluble and water-soluble products obtained from the sulfuric acid refining of petroleum lubricating oils. V

The invention will be described in connection with the following specific examples in which the assays are made by differential microscopic count in a briquette made up with a thermosetting resin and polished; the so-called Rosiwal method of analysis. In this case, the method did not take into account the transparent gangue particles but as their amount is negligible, amounting normally to less than a few per cent, they are without significance. The accuracy of the analysis should not be considered as much greater than the nearest 2% where a large amount of one constituent is being measured.

This application is, in part, a continuation of our co-pending application, Serial No. 777,858, filed October 3, 1947, now abandoned.

Example 1 A badly contaminated mixed magnetite-ferrosilicon medium containing magnetite and ferrosilicon in the ratio of 42 to 58 was deslimed, conditioned for 2 minutes at 70% solids with 3 lb./ton sulfuric acid, 2.4 lb./ton oil-soluble petroleum sulfonate from the refining of lubricating oil stocks from a California crude, and 2 lb./ton of a 22.B. fuel oil. The pulp was then diluted Contaminated medium used in Examplel was subjected to the same treatment except that the 6 reagents were increased to 4 lb./ton of sulfuric acid, 3.2 lb./ton of petroleum sulfonate and 3 lb./ton of fuel oil. The rougher concentrate was also subjected to a final cleaning operation. The metallurgical results are as follows:

Per Cent Mag. and

Product Weight Hematite Fesl Head 100. 00 42 58 C1. Concentrate. 42. 76 82 17 0]. Tail 5. 43 FeSi Tail 47. 63

Ercample 3 Per Cent Weight Proportions Product Weight of Magnetite to FeSi 17. 81 91. 0 9.0 5. 20 FeSi Tail 73. 99

Example 4 A mixed ferrosilicon-magnetite operating medium containing about 39% ferrosilicon and 61% magnetite was conditioned at 50% solids with 7.2 lb./ton sulfuric acid, diluted, deslimed, washed, and again conditioned at 70% solids with 2 lb./ton of sulfuric acid, 6 lb./ton of the petroleum sulfonate used in Example 2- and 3 lb./ton of fuel oil. The pulp was diluted to 18% solids and floated, the rougher concentrate being cleaned and recleaned. Slightly under one-half the weight of the feed was obtained in a concentrate having just under 99% magnetite and just over 1% ferrosilicona The metallurgical results are as follows:

Per Cent Weight Proportions of Pmduct Weight Mag.andHem.toFeSi Head 100.00 60. 9 39. 1

Mag. Concentrate 46. 37 98. 8 1.2

2nd 01. Tall... 2.61

1st C1. Tail 4. 42

FeSi Tail 43. 44

Example 5 V The contaminated ferrosilicon-magnetite medium of Example 4 was subjected to a procedure similar to Example 4 but with slightly different amounts of reagents, namely, 3 lb./ton sulfuric acid and 5.6 lb./ton petroleum sulfonate in the second1conditiohing step. A microscopic assay was made of all of the fractions instead of. just '2 the'mag'netite concentrate; The metallurgical resultsare as follows:

' 'Per Cent Weight Proportionsof Product Weight Magand Hem.toFeSi Head 100. 60. 9 39. 1

Mag. Concent te. 45. 06 99.1 0.9

Comb. C]. Tal 8. 31 59. 9 40. 1

F961 Tail 44. 51 20. 6 79. 4

Example 6 Per Cent Estimated Per Cent Product Weight Magnetite and FeSi He 100. 00 58 42 C1. Concentrate" 38.54 98 2 2nd 01. Ta 10.76 95 5 1st Cl. Tail 24. 48 35 65 FeSi Tail 26.22 5 95 Example 7 A further portion of the contaminated medium of Example 6 was conditioned at 75% solids with 4 1b./ton of sulfuric acid, 2 lb./ton of sulfonated talloel and 3.3 lb./ton oflight fuel oil. After dilution to 18% solids, flotation was effected in a circuit having a pH of 4.4. The flotation concentrate wascleaned once after conditioning with an additional 1 1b./ ton of sulfuric acid and 0.08 113/ ton of pine oil. The cleaner concentrate was subjected to microscopic assay and constituted 34.72% ofthefeedwith a distribution of 99% magnetite and 1% ferrosilicon. In View of the extremely high grade of the concentrate the cleaner tailing and rougher tailing were not subjected to microscopic assay.

Example 8 A ferrosilicon medium which had become contaminated with magnetite during the treatment of a magnetite-containing hematite iron ore was treated. The ratio of ferrosilicon to magnetite was 28:72 by weight. Treatment with oil, or water-soluble petroleum sulfonates, essentially as described in the above examples, gave magnetite concentrates containing about 45% of the total weight and having a magnetite to ferrosilicon ratio of about 99:1 by weight.

Attempts were made to use talloel as a promoter for the magnetite in this medium without the use of sulfuric acid and fuel oil. Conditioning at high solids with l.0-2.0 lb./ton talloel gave a non-selective float resulting in a concentrate highly contaminated with ferrosilicon so that the magnetite to ferrosilicon ratio was" not sufficiently-improved to allow reuse or the me- Ewample 9 A 50/50 mixture of fresh ferrosilicon and magnetite of the particle size used in heavy media was'conditioned at high solids with 2.5 l b../ton of an oil-soluble petroleum sulfonate, 1.0 lb./ton fuel oil and 2.0 1b,./ton sulfuric acid. After dilution to. 22% density, it was subjected, to froth flotation. About 50% of the mixture floated as a flotation concentrate, which had substantially the same compositionas the flotation feed when examined visually under the microscope.

When the oil-soluble petroleum sulfonate was replaced with 3.5 lb./ton of water-soluble petroleum sulfonate, and the fuel oil increased to 3.0 lb./ton, 49% of the. mixture floated as a concentrate', showing no substantial difference in composition from the feed.

When the mixture was changed to fresh ferrosilicon and 15% fresh magnetite, non-selective flotation still resulted with about half of the mixture floating without substantial change in composition.

Example 1 0 The behavior of fresh ferrosilicon and fresh magnetite with other well-known anionic flotation agents was investigated. When fresh ferrosilicon alone was floated with 0.096 lb./ton oleic acid, 87.5% of the ferrosilicon floated as a concentrate.

When fresh magnetite was floated with staged additions of 0.1 lb./ton of oleic acid until a total of 0.5 lb./ton was reached, only a little over 10% of thema netite floated.

When a 50/50 mixture .of fresh ferrosilicon and fresh magnetite was floated with two staged additions of 0.1 lb./ton of oleic acid, only about 4% of the feed floated in a non-selective float.

Similar results were obtained when talloel was substituted for oleic acid.

W la m:

1. A method of separating magnetite from a mixed ferrosilicon-magnetite heavy media that has been used in the concentration of ores containing natural magnetic materials for such time that the ferrosilicon constituent has a relatively low fioatability with anionic sulfonated flotation reagents; which comprises conditioning said heavy media at high solids with a sulfonated collector for oxidized iron minerals and a strong acid substance having a dissociation constant of at least l0-", the amount of said acid substance being Such that on dilution to froth flotation density and floating, the rougher tailing, in the absence of added a a sh ws a pH i h r n of two, to six; and subjecting the aqueous pulp of the heavy media thus treated to froth flotation; the major constituent of the collector beingselected from the group consisting of oilsoluble and Water-soluble petroleum sulfonates obtained in the refining of petroleum lubricating oils, sulfonated fatty acids, and sulfonated glyceride oils; and removing a froth concentrate having a very high concentration of magnetite and a very low concentration of ferrosilicon, and a tailing having a high concentration of ferrosilicon.

2. A method according to claim 1 in which the major constituent of the collector is a watersoluble petroleum sulfonate.

3. A method according to claim 1 in which the major constituent of the collector is an oil- .soluble petroleum sulfonate. 4. A method according. to claim 1 in which the sulfonated talloel is the sulfonated fatty acid.

7. A method according to claim 1 in which said strong acid substance is sulfuric acid.

SWAIN JOS PH SWAINSON. EARL CONRAD HERKENHOFF. RICHARD HAROLD LOWE.

REFERENCES CITEI The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,656,270 Downs Jan. 17, 1928, 2,341,247 Trostler Feb. 8, 1944 2,385,054 Booth Sept; 18, 1945 2,410,376 Booth Oct. 29, 1946 2,410,377 Booth Oct. 29, 1946 2,414,714 Booth Jan. 21, 1947 2,439,200 Booth Apr. 6, 1947 2,430,762 Erck Nov. 11, 1947 2,497,790 Pauvrasseau Feb. 14, 1950 

1. A METHOD OF SEPARATING MAGNETITE FROM A MIXED FERROSILICON-MAGNETITE HEAVY MEDIA THAT HAS BEEN USED IN THE CONCENTRATION OF ORES CONTAINING NATURAL MAGNESTIC MATERIALS FOR SUCH TIME THAT THE FERROSILICON CONSTITUENT HAS A RELATIVELY LOW FLOATABILITY WITH ANIONIC SULFONATED FLOTATION REAGENTS; WHICH COMPRISES CONDITIONING SAID HEAVY MEDIA AT HIGH SOLIDS WITH A SULFONATED COLLECTOR FOR OXIDIZED IRON MINERALS AND A STRONG ACID SUBSTANCE HAVING A DISSOCIATION CONSTANT OF AT LEAST 10-7, THE AMOUNT OF SAID ACID SUBSTANCE BEING SUCH THAT ON DILUTION TO FROTH FLOTATION DENSITY AND FLOATING, THE ROUGHER TAILING, IN THE ABSENCE OF ADDED ALKALI, SHOWS A PH IN THE RANGE OF TWO TO SIX; AND SUBJECTING THE AQUEOUS PULP OF THE HEAVY MEDIA THUS TREATED TO FROTH FLOTATION; THE MAJOR CONSTITUENT OF THE COLLECTOR BEING SELECTED FROM THE GROUP CONSISTING OF OILSOLUBLE AND WATER-SOLUBLE PETROLEUM SLUFONATES OBTAINED IN THE REFINNING OF PETROLEUM LUBRICATING OILS, SULFONATED FATTY ACIDS, AND SULFONATED GLYCERIDE OILS; AND REMOVING A FROTH CONCENTRATE HAVING A VERY HIGH CONCENTRATION OF MAGNETITE AND A VERY LOW CONCENTRATION OF FERROSILICON, AND A TAILING HAVING A HIGH CONCENTRATION OF FERROSILICON. 